Gas filtration media are known. For example, see U.S. Pat. Nos. 5,507,847 and 6,409,785. U.S. Pat. No. 5,507,847 discloses an ultra-low penetration air (ULPA) filter. This filter includes at least one mircoporous filtration layer sandwiched between one or more layers of an upstream and downstream support material. The microporous layer may be made of, among other things, expanded polytetrafluoroethylene (ePTFE) or ultra high molecular weight polyethylene (UHMWPE). U.S. Pat. No. 6,409,785 discloses a high efficiency particulate air (HEPA)-rated filtration media including a porous primary filtration layer. The porous primary filtration layer is an ePTFE. Additionally, it is known to use ePTFE supported by microglass.
The use of ePTFE in such media, while capable of achieving the needed removal efficiencies, is expensive and is difficult to process because of its lack of mechanical strength.
While, U.S. Pat. No. 5,507,847 mentions that microporous membranes of UHMWPE may be suitable, no such membranes are disclosed. U.S. Pat. Nos. 3,351,495 and 4,833,172 disclose UHMWPE membranes, but these membranes are suggested for different uses, such as a liquid filtration media or a battery separator or a breathable coating for textiles.
Therefore, there is a need for a new gas filtration media based upon UHMWPE membranes.